I've seen an interesting television program about this case. From the article at the above link, under "Literature and Film":

"This exorcism case inspired the 1971 novel The Exorcist by William Peter Blatty, which in turn was adapted into the classic 1973 horror film of the same name.[11] The case also inspired the 2000 movie Possessed, which is said to be closer to the story in Allen's book.[11] A documentary was also made of the case, titled In the Grip of Evil.[12] Another documentary movie was made in 2010 named "The Haunted Boy: The Secret Diary of the Exorcist" where a group of investigators travels to the location in question and uncovers the diary that is said to be kept by William S. Bowdern.[13]"

Hi PC
I just read your link-I thought the boy lived in Georgetown DC?

__________________"Is all that we see or seem
but a dream within a dream?"
-Edgar Allan Poe

"...the man and the peaked cap he is said to have worn
quite tallies with the descriptions I got of him."
-Frederick G. Abberline